Seed size and mass in relation to environment

Abstract Propagule masses are here recorded for shade-tolerant species belonging to 20 genera which show an average of about three-and-one-third times the mass of the propagules of co-generic species of open habitats. These are additional to the 30 genera already reported on by the author. Propagules of cornfield weeds belonging to 18 genera are shown to exhibit greater masses than their congeners, even though some of these are shade-tolerant, and this, it is suggested, may be the outcome of the prolonged selective effect of ‘winnowing’. Other causes of heavy propagules of open-habitat species are suggested, indicative of natural selection.